Process for producing dilithio hydrocarbons

ABSTRACT

Dilithio hydrocarbons are produced by heating allyllithium or a hydrocarbon-substituted allyllithium for 20-200 hours at 50*150* C. Substituted allyllithiums can have alkyl groups or aryl groups, but must have replaceable allylic hydrogen. The products are useful as iniators for polymerization.

United States Patent [191 Antkowiak PROCESS FOR PRODUCING DILITHIOHYDROCARBONS [75] Inventor: Thomas A. Antkowiak, Cuyahoga Falls, Ohio[73] Assignee: The Firestone Tire & Rubber Company, Akron, Ohio [22]Filed: April 14, 1971 [21] Appl. No.2 134,059

[56] References Cited UNITED STATES PATENTS 2/1956 Londergan ..260/665 R4/1963 Seyferth et a1 ..260/665 R 1 Feb. 27, 1973 OTHER PUBLICATIONSMark. Encyclopedia of Polymer Science and Technology IntersciencePublishers New York, N.Y. 1964, Vol. 1, p. 644

Strohmeier et a1. Z. Fu Elektrochemie 66, (1962) p. 823-7.

Primary Examiner-Patrick P. Garvin Assistant Examiner-A. P. DemmersAttorney-S. M. Clark and Gordon B. Seward [57] ABSTRACT Dilithiohydrocarbons are produced by heating ally]- lithium or ahydrocarbon-substituted allyllithium for 20-200 hours at 50-150 C.Substituted allyllithiums can have alkyl groups or aryl groups, but musthave replaceable allylic hydrogen. The products are useful as iniatorsfor polymerization.

5 Claims, No Drawings PROCESS FOR PRODUCING DILITHHO HYDROCARBONSBACKGROUND OF THE INVENTION This invention relates to a method forproducing lithiated hydrocarbons. More specifically, it relates to amethod for producing various dilithio hydrocarbon compounds which areuseful as initiators for polymerization of a variety of monomericmaterials.

It is known that compounds such as trans-stilbene can be lithiated byreacting them with a. lower-alkyl monolithium compound in a polarsolvent medium. It is difficult, however, to remove the last traces ofthe polar solvent, and its presence affects the microstructure of dienepolymers initiated with the lithiated products.

Other investigators have di-, tri-, and tetra-lithiated acetylenes byreacting acetylenes, in hydrocarbon solvent, with an alkyl mono-lithiumcompound. This reaction forms mixtures of the variously lithiatedacetylenes, which are extremely difficult to separate. The lithiatedacetylenes are not effective as polymerization initiators for conjugateddienes. Additionally, the acetylenic starting materials are chemicalspecialties which are very expensive, and not available in quantity.

Accordingly, a need exists for a process for preparing dilithiohydrocarbons without the various difficulties and drawbacks present inknown processes.

SUMMARY OF THE INVENTION It is an object of the instant invention toprovide a method for preparing dilithio hydrocarbon compounds fromreadily available reactants, which compounds can serve as usefulinitiators for polymerization. It is another object of this invention toprovide a method for dilithiating hydrocarbons in a simple,straightforward reaction, producing a satisfactory yield of the desiredproduct with a minimum of difficulty.

These and other objects are accomplished by the instant invention which,stated simply, provides a method for producing dilithio hydrocarbons byheating a compound which is allyllithium or a hydrocarbon-substitutedallyllithium which contains allylic hydrogen in the hydrocarbonsubstituents, the heating being per formed at a temperature of from 50to 150 C., preferably from 80 to 100 C., for a period of from 20 to 200hours. Substituted allyllithium compounds which contain from four up to100,000 or more carbon atoms can be used effectively. The hydrocarbonsubstituents can be straight chain or branched chain saturated aliphaticgroups, or saturated cyclo-aliphatic groups or aryl groups. A minimum ofolefinic unsaturation should be present in the substituents.Combinations of two or more of these types of substituents can bepresent.

The heating step acts to produce dilithio hydrocarbons, but alsoproduces some lithium hydride and various non-lithiated hydrocarbons.These by-products need not be removed from the desired dilithiohydrocarbon product, as they are not harmful to polymerizationreactions.

Among the lower molecular weight substituted allyllithium compoundswhich can be used as starting materials, the reaction products ofsecondary or tertiary butyllithium with isoprene or butadiene-l,3 areespecially recommended.

By reacting, for example, equimolar amounts of secbutyllithium withbutadiene-l,3, the principal product formed isl-lithio-5-methyl-2-heptene (both cis and trans isomers). Similarly,equimolar amounts of sec-butyllithium and isoprene react to produceprimarily llithio-3,S-dimethyI-Z-heptenes. Since the reactants arereadily available commercially, these starting compounds are quiteuseful in the method of the invention.

The dilithio compounds of the invention are particularly useful asinitiators for producing block polymers having a central elastomericblock and terminal thermoplastic blocks. Typical of these polymers is anS-B-S triblock polymer, with the B representing a central block ofbutadiene homopolymer, with terminal blocks of styrene homopolymerrepresented by the S segments. In this case, the butadiene block isfirst formed, using a dilithio initiator. When the central block isformed, the polymer chains have two live ends, onto which the styrenehomopolymer blocks are polymerized, by charging styrene monomer afterall of the butadiene monomer has polymerized.

DESCRIPTION OF PREFERRED EMBODIMENTS The starting compound in the methodof the invention is described generally as allyllithium, or ahydrocarbon-substituted allyllithium which contains allylic hydrogen butlittle olefinic unsaturation in the hydrocarbon substituents. By reasonof its structure, the compound has a lithium atom in the allylicposition, that is, on a carbon atom which is adjacent to a carbon atomhaving a double bond attached thereto. Additionally, the compoundcontains replaceable allylic hydrogen. The compound can be the basicthree-carbon compound allyllithium, or can contain hydrocarbonsubstituents up to as much as 100,000 or more carbon atoms, in the rangeof high polymers. The hydrocarbon substituents can be alkyl, aryl orcycloalkyl radicals, and should contain a minimum of olefinicunsaturation.

The substituted allyllithium compounds have the general formula:

with the R's indicating possible substitution points. The carbon atomsare numbered for clarity. If either R or R is hydrogen, then thecompound contains allylic hydrogen, and is within the scope of theinvention as starting material. If R R or R is a hydrocarbon radical,the carbon atom which attached to C, (in the case of R, and R or to C(in the case of R is in the allylic position, and can carry allylichydrogen. Of course, if 1R R or R is a phenyl group or a tertiary carbonatom no allylic hydrogen will be present at these substituent points.

From the foregoing it can be seen that there are a very large number ofsubstituted allyllithium compounds which will serve as startingcompounds for the method of the invention. Most of the low-molecularweight compounds produce dilithio initiators which are relativelyinsoluble in the hydrocarbon solvents normally used for polymerizingconjugated dienes and/or styrene. Where greater solubility is desired,those compounds having larger hydrocarbon substituent groups yielddilithio initiators which tend toward increased solubility inhydrocarbon solvents. Similarly, aryl substituents can affect thebehavior of the dilithio initiators in contact with styrene and suchdiluents as benzene or toluene.

Particularly recommended as starting compounds are the reaction productsof conjugated dienes having four to carbon atoms with secondaryortertiary monolithio alkane compounds of from three to carbon atoms.

The lithio alkanes which can be employed include, for example:

l-methyll -lithioethane l-methyll -lithiopropane 1,1-dimethyll-lithioethane 2-lithiopentane 3-lithiopentane 2-methyl-2-lithiobutane2-methyl-3-lithiobutane 2-methyl-4-lithiopentane3-methyl-3-lithiopentane 2-metl1yl-3,3-dimethyl-2-lithiobutane3,3-diethyl-2-lithiopentane 2-lithioundecane and the like.

Preferred are l-methyll -lithioethane l-methyll -lithiopropane, and

l ,1-dimethyl-l-lithioethane Conjugated dienes which can be used in thefirst step include:

l,3-butadiene isoprene 2,3-dimethyl-l ,B-butadiene 1,3-pentadi'ene(piperylene) 3-methyl-l ,3;pentadiene 1,3-heptadiene 3,4-dimethyl-l,S-hexadiene and the like.

Preferred conjugated dienes are l,3-butadiene isoprene piperylene 4 Thereaction can be performed at a relatively low temperature, from -30 to 0C., and this reaction will proceed to completion in 20 to 100 hours,forming a hydrocarbon-substituted allyllithiumcompound. Temperaturesabove 0 C. tend to promote the formation of oligomers, with 2 or moremolecules of the conjugated diene reacting with 1 molecule of themonolithio alkane. Generally, equimolar amounts of the two reactants areemployed, although a slight excess of conjugated diene is notparticularly harmful. An excess of monolithio alkane should be avoided,since the presence of monolithio hydrocarbons in the reaction product isundesirable.

The substituted allyllithium compound produced in the first step is thenheated at a temperature of from 50 to 150 C., preferably from 80 to 100C. for a period of from 20 to 200 hours. The heating step appears tocause the compound to undergo a self-metalation reaction, forming asubstantial proportion of dilithio hydrocarbon. During the heating stepa loss of carbon-bound lithium is observed, as measured by the modifiedGilman titration described by Turner et al. in

Rubber Chemistry and Technology, 42, 1054 (1969). It is hypothesizedthat this loss is due to formation of lithium hydride, as evidenced bythe production of hydrogen on hydrolysis. AFter prolonged heating theamount of carbon-bound lithium remaining can approach 50 percent.

Both the first step and the subsequent heating step can be performed inthe presence of 'an inert diluent, such as lower aliphatic hydrocarbons,to improve heattransfer and assist in product separation. Hexanes,heptanes and the like are preferred.

If the dilithio products formed are insoluble in the mixture produced(which can include inert diluents), they can be separated by filtrationif desired. However, separation is not generally necessary, since thebyproducts of the reaction are not generally harmful to subsequent useof the dilithio product.

Other dilithio hydrocarbons can be similarly prepared by heat-treatingany of the substituted allyllithium compounds as defined generallyabove.

Additional substituted allyllithium compounds which can be used include:

l-lithio-3 ,3-dimethyl-2-hexene l-lithio-3,3-diphenyl-2-propene2-lithio-5-methyl-3-pentene 2-lithio-2,5-dimethyl-3-hexene2-lithio-2-methyl-3-heptene 1-lithio-2-methyl-2-propenel-lithio-2-vinylpentane A better understanding of the method of theinvention can be obtained by reference to the following examples, inwhich all percentages are by weight, unless otherwise indicated. Theexamples are included for illustrative purposes, and are not to beconstrued as limiting the scope of the invention, which is defined bythe appended claims.

EXAMPLE I Equimolar amounts of sec-butyllithium and 1,3-butadiene werecombined and sealed in a series of nitrogen-filled tubes. The tubes wereagitated at 25 C. The reaction progress was followed by periodicallyquenching the contents of an individual tube in water at 0 C., andanalyzing the hydrocarbons by gas chromatography. At 24-36 hours, nomore butane was found in the chromatograph of the hydrolysate,indicating that essentially all the sec-butyllithium had reacted.

At this point, the composition of the contents of the tubes afterhydrolysis was shown in Table 1, following.

TABLE 1 Material Weight trans-S-methyl-Z-heptene 62.5cis-S-methyl-Z-heptene l9.4 5-methyll -heptene 6.2 G12 and C-l6hydrocarbons 12.0 Total 100.1

The first three compounds listed in Table l were all identified asmonoolefinic C-8 hydrocarbons. The amount of the first two compounds wasdetermined by gas chromatographic techniques, and the structureassignments were made by infra-red and NMR spectrometry. The third C-8isomer amount was obtained by difference.

It was seen that the bulk of the product was in the form of C8monoolefins, suggesting it to be the product of the addition ofequimolar quantities of the two reactants. The Cl2 and C16 products,similarly, appear to be the result of the addition of two and threebutadiene units respectively to sec-butyllithium.

EXAMPLE II In order to study the behavior on heating of the reactionproducts produced in Example I, sealed tubes were prepared as before,charged with equimolar amounts of sec-butyllithium and 1,3-butadiene.After 30 hours at 25 C., the tubes were warmed to room temperature, andthen placed in a bath at 80 to 100 C. It was noticed that a white solidprecipitated on warming to room temperature.

On further heating in the bath, a greatly increased amount of solid wasobserved, and the solution assumed a dark, red-br0wn color.

The progress of the heating reaction was followed by periodic titrationsfor carbon-bound lithium, using the modified Gilman titration method ofTurner et al. in Rubber Chem. & Tech. 42, 1054 (1969). At 80 C. thelevel of carbon-bound lithium dropped to about 70 percent after 60hours, and to about 60 percent after 120 hours, based on the originalcontent. At 100 C. the level was about 60 percent after hours, and downto about 40 percent after 140 hours. At both temperatures the percentageof remaining carbon-bound lithium appeared to level off after an initialrapid drop.

The products of the heating reaction were hydrolyzed as before, using D0 as well as H O. Analysis of a sample after the step of warming to roomtemperature, but before heat-treatment, showed no apparent chemicalchange during the warming step.

Reactants which had been heat-treated to reduce their carbon-boundlithium to 50 percent of its original value were then studied. Thesolid, insoluble,portion was first separated from the liquid byfiltration. Each of these phases was then hydrolyzed, a portion with H0, and another portion with D 0. The resultant hydrocarbons wereanalyzed by mass spectroscopy.

Mass spectroscopy of the solid portion which had been hydrolyzed with P10 showed C8 hydrocarbons with molecular weights of 112. The solidportion which was hydrolyzed with D 0 showed C8 hydrocarbons withmolecular weights of 114. From these figures, the solid portion wasconcluded to be dilithiated C8 compounds.

Similar mass spectroscopy investigation of the filtrate yielded C8hydrocarbons of 112 molecular weight when treated with either H O or D0, indicating that the filtrate consisted of non-lithiated C8 products.

In a similar manner, the C1 2 portion of the product was shown to bedilithiated. Analysis of the C1 6 portion was made considerably moredifficult by the complexity of the mixture of isomers.

In the preceding examples the monolithio hydrocarbons of the compoundsproduced are shown to be the product of the reaction of substantiallyequimolar amounts of a monolithio alkyl hydrocarbon and a conjugateddiene. Both the reactants were four-carbon compounds, and the productconsisted principally of monolithiated C 8 hydrocarbons, indicatin aone-toone molar addition of the reactants pre ominated.

However, the presence of Cl2 and Cl6 compounds in the product showedthat two or more molecules of the conjugated diene can add to themonolithio alkyl, and produce a series of monolithio hydrocarbons.

On subsequent heating, a mixture of C8, C1 2, and Cl6 dilithiohydrocarbons is formed which are all effective initiators ofpolymerization. While additional olefinic unsaturation is present in theCl2 and Cl6 dilithio hydrocarbons as a result of the addition of two andthree molecules of butadiene, respectively, no appreciable amount ofpolylithiated compounds is found. Hence, the higher molecular weightproducts which can be produced in the method of the invention are alsouseful, as well as those compounds which are oneto-one additionproducts. If desired, however, these higher molecular weight productscan be separated out by any convenient means.

I claim:

l. The method of producing dilithio hydrocarbons by heating allyllithiumor a hydrocarbon-substituted allyllithium which contains allylichydrogen in the hydrocarbon substituents at a temperature of from 50 to150 C. for 20 to 200 hours, wherein the hydrocarbon-substitutedallyllithium is the product of the reaction of a secondary or tertiarymonolithio alkane of from three to 20 carbon atoms with a conjugateddiene of from 4 to 10 carbon atoms, said reaction being performed atfrom "30 to 0 C. for a period of from 20 to 100 hours.

2. The method of claim ll, wherein the monolithio alkane issec-butyllithium or tert-butyllithium.

3. The method of claim 1, wherein the conjugated diene is isoprene orbutadienel ,3.

4. The method of claim 1, wherein an inert hydrocarbon diluent ispresent.

5. The method of claim 1, wherein the heating is performed at from to C.

2. The method of claim 1, wherein the monolithio alkane issec-butyllithium or tert-butyllithium.
 3. The method of claim 1, whereinthe conjugated diene is isoprene or butadiene-1,3.
 4. The method ofclaim 1, wherein an inert hydrocarbon diluent is present.
 5. The methodof claim 1, wherein the heating is performed at from 80* to 100* C.